1. Field of the Invention
The present invention relates to an ink set for inkjet recording, and an image recording method and apparatus, and more particularly to an ink set for inkjet recording, an image recording method and apparatus which satisfy the requirements of achieving high fixing characteristics, increasing the reproduction range of secondary colors, and ensuring optical density and preventing bleeding in the case of high-speed printing.
2. Description of the Related Art
Various recording media have come to be used as inkjet recording media, and there are demands for high-quality image formation even when using standard commercial paper. On the other hand, with regard to the ink, a pigment is desirable as an ink material which ensures good image fastness, such as waterproofing or light resistance, and various investigations have been carried out in this respect. However, if recording is carried out onto normal paper, then problems may arise in the form of significant bleeding, and inadequate coloring density and fixing properties. There have also been demands from users for higher speed operation in inkjet recording, and high-speed printing capability is also demanded in single pass methods which are capable of recording by means of a single scan of the head, as well as in shuttle scanning systems.
As a means for preventing bleeding and improving coloration density on normal paper, a method is known which brings a liquid composition that reacts with the ink into contact with the ink (i.e., mixes the liquid composition with the ink), on the recording medium. Two typical examples of this are shown below.
(1) A method has been proposed in which, in order to mix a liquid composition that reacts with the ink, on the recording medium, and to improve image density, improve water resistance and suppress bleeding, a liquid composition which ensures a satisfactory image is applied to the recording medium before or after spraying ink for recording the recorded image. For example, Japanese Patent Application Publication No. 2004-10633 discloses an ink set having excellent optical density, bleeding characteristics, color mixing characteristics, and drying time, by using a liquid composition which has an action of causing the pigment to aggregate. However, it has been found that this cannot be regarded as satisfactory from the viewpoint of fixing characteristics and color reproduction (especially in respect of the reproduction of secondary colors).
(2) As a method for mixing an ink and a liquid composition containing very fine particles, on the recording medium, it has been proposed to use a combination of an ink containing a very fine particle pigment and an aqueous liquid composition containing very fine particles having their surfaces charged to the opposite polarity with respect to the ink, in a dispersed state. For example, Japanese Patent Application Publication No. 2003-39810 discloses a method which achieves a broad color reproduction range on normal paper, and eliminates color non-uniformities or bleeding, by using a pigment having an average particle size of 60 nm or less and a cumulative 90% particle size in the volume particle diameter distribution of 100 nm or less. However, it has been judged that this is not of a satisfactory level from the viewpoint of optical density or bleeding in the case of high-speed printing involving consecutive ejections of adjacent dots, which is essential in single pass recording.
Furthermore, Japanese Patent Application Publication No. 2003-3095, for example, discloses forming a pigment to a very fine particle size in order to achieve good coloration characteristics in an aqueous pigment-based ink, and to improve the scratching resistance of the image portion, in other words, to improve fixing characteristics. It is proposed that the average particle size of the pigment should be in the range of 50 to 100 nm, and that 50% or more of the dispersed pigment in the particle size distribution should be in the range of 50 to 150 nm.
In view of this background, the present inventor used the pigment-based ink according to Japanese Patent Application Publication No. 2003-3095 in the method (1) described above, which mixes an ink with a liquid composition that reacts with the ink on the recording medium; however, it was found that this was not of a satisfactory level from the viewpoint of the fixing characteristics and color reproduction (and in particular, reproduction of secondary colors).